The present invention relates to high-pressure hydraulic drives and actuators, and, more particularly, it relates to pressure valves.
The present invention can be used to utmost effectiveness in the hydraulic circuitry of powered mine roof supports, e.g. as the hydraulic lock of a hydro-operated mine roof support prop.
However, the invention can be utilized in various other industries and technologies, wherever a pressurized fluid is to be reliably sealed in a space or spaces of a mechanism, with subsequent gradual relieving of this pressure.
The invention is capable of being incorporated both in hydraulic systems and in pressurized-gas ones, e.g. pneumatic systems.
At present, there is known a variety of structures of pressure valves, sometimes also called hydraulic fluid locks, employed to control various elements of fluid systems.
Thus, there is known a hydraulic lock disclosed in the GB Pat. No. 1,188,022, comprising a housing with passages, the counterbore of this housing accommodating therein a spring-urged pressure-relief piston and a valve seat engageable by a closure member having a tapering surface. There is also incorporated a stepped-diameter sleeve biased by a spring relative to the housing of the hydraulic lock and having a throttling opening or orifice. The closure member is biased by a spring from the stepped-diameter sleeve and has its opposite end engaged by the end face of the pressure-relief piston.
In the normal position, the closure member and the stepped-diameter sleeve are urged against the seat by the efforts of the spring and of the pressure of the working fluid in the vessel or volume where the hydraulic lock is mounted, which prevents leaking of this fluid.
With the vessel or volume being filled, the working fluid in the supply passage or duct acts upon the closure member and displaces it jointly with the stepped-diameter sleeve, whereby a fluid passage is defined between the closure member and the seat.
To relieve the vessel or volume from the pressure, the working fluid is fed to the end face of the pressure-relief piston, whereby in its motion the pressure-relief piston acts upon the closure member, pulling it along, and so the working fluid starts flowing to drain via the throttling opening in the stepped-diameter sleeve which is in the meantime urged by the pressure and by the spring against the seat, and via the clearance formed between the closure member and the seat, so that the pressure is gradually reduced.
With the pressure having been reduced to a level when the pressure-relief piston is capable of moving or rising still further and of displacing the stepped-diameter sleeve, thus increasing the flow passage area between the closure member and the seat, the pressure-relieving action is intensified.
However, the hydraulic lock of the abovedescribed structure is both complicated and inadequately reliable in its performance. The major cause of failures of this hydraulic lock in operation has proved to be the clogging of the throttling opening, so that the pressure-relieving action becomes impossible.
There is further known a hydraulic lock (see the description of OMKTM Mine Roof Support in "Hydraulic Actuators of Powered Mine Roof Supports and Their Development Trends" by V. V. Vavilov, T. E. Ladokhina et al., in Russian, Moscow, 1971, p.15) comprising a housing with a high-pressure space and a low-pressure space separated by a partition with an axial opening or bore receiving therein a reciprocable longitudinal cylindrical valve member having a blind axial passage made in the body thereof, as well as radial openings via which the two spaces can be alternately in communication upon the displacement of the valve member; a pressure-relief piston biased by a spring is mounted in the low-pressure space and cooperates with the valve member, as the pressure-relief piston is displaced by the pressure of the liquid supplied to act upon the end face thereof, remote from the valve member. The valve member carries sealing means adapted to seal off the associated volume or vessel upon its having been filled with the working liquid from the supply source, and a sleeve biased by a spring protecting the sealing means from damage during the reciprocation of the valve member.
As the working liquid is supplied under pressure into the volume or vessel incorporating the hydraulic lock, the valve member is displaced by the action of this pressure. Upon the sealing means on the valve member having cleared the surface of the opening in the partition, the liquid flows into the high-pressure space via the blind axial passage and the radial openings.
To relieve the vessel or volume from the pressurized liquid, the working liquid is fed to act upon the end face of the pressure-relief piston, so that the latter's opposite end acts upon the valve and displaces it axially. Upon the sealing means on the valve member having cleared the lateral surface of the opening or bore in the partition, the high-pressure space communicates with the low-pressure space, whereby the pressure reduction and the relieving of the vessel or volume are commenced.
A major shortcoming of the last-described structure of a hydraulic lock is that when the vessel or volume is to be relieved from pressure, the hydraulic lock opens in a relatively short time, whereby hydraulic impact or shock takes place both in the low-pressure space and in the high-pressure space. This surging shock may result in the pressure being momentarily built up to a value which is three times as high as the initial pressure in the vessel or volume. The process is accompanied by oscillation of the valve member in the housing of the hydraulic lock at a frequency up to 120 Hz and velocity up to 1000 mm/sec. This results in intensive wear of the hydraulic lock and its relatively rapid failure.
There is further known a hydraulic lock which is currently widely used in powered mine roof supports for controlling the operation of hydraulic props (see the description of the EKOR Hydraulic Lock in "Hydraulic Actuators of Powered Mine Roof Supports and Their Development Trends" by V. V. Vavilov, T. E. Padokhina et al., in Russian, Moscow, 1971). The hydraulic lock comprises a housing with a high-pressure space and a low-pressure space. In the counterbores of the housing there are accommodated a pressure-relief valve biased by a spring and a plastic seat engageable by a closure member in the shape of a ball urged against the seat by an abutment biased by a spring. When the working liquid is fed into the hydraulic prop, the pressure of the supplied liquid drives the ball away from the seat, opening the path for the liquid into the prop.
To relieve the pressure, the working liquid is fed to the end face of the pressure-relief valve which is thus displaced and acts by its opposite end upon the ball, making the latter clear its seat, whereby the working liquid is drained from the hydraulic prop.
With the hydraulic lock having the last-described structure, a hydraulic shock likewise takes place, resulting in an increased pressure and an oscillation mode of the operation of the ball, the oscillation having a relatively high frequency, which results in accelerated wear of the components of the hydraulic lock, particularly, of the seat.
There is still further known a pressure valve employed for controlling the operation of the hydraulic props of powered mine roof supports (see, for instance, the SU Inventor's Certificate No. 513,171), comprising a housing with a high-pressure space and a low-pressure space. The two spaces are separated by a partition having a central opening or bore accommodating therein a movable cylindrical valve member with sealing means. Made in the body of the valve member are passages through which the spaces alternatingly communicate when the valve member is displaced.
A pressure-relief valve biased by a spring is mounted in the low-pressure space of the housing.
In the normal position of the valve, the sealing means carried by the valve member engage the lateral surface about the bore in the partition and seal away one space from the other space.
When the working liquid is to be fed into the under-piston space of the hydraulic prop to extend the latter, the working liquid is fed into the hydraulic lock, the pressure of the liquid displacing the valve member toward the high-pressure space, whereby the two spaces communicate, and the liquid flows through the valve into the under-piston space of the hydraulic prop. With the required pressure built up in the under-piston space of the hydraulic prop, the feeding of the liquid into the hydraulic lock is discontinued, whereby the action of the liquid pressure in the under-piston space and of the return springs restores the valve member to its normal position where it separates the high-pressure space from the low-pressure space and locks the liquid in the under-piston space of the hydraulic prop.
To relieve the hydraulic prop from the pressure, the working liquid is fed to the end face of the pressure-relief piston, opposite to the one cooperating with the valve member, whereby the pressure displaces the pressure-relief piston which moves the valve member, overcoming the action of the liquid pressure in the high-pressure space and of the return springs. Upon the sealing means having cleared the lateral surface of the bore in the partition, the two spaces communicate with each other, and the fluid under pressure is drained from the under-piston space of the prop through the hydraulic lock into the drain line, relieving the hydraulic prop.
The relieving of the hydraulic prop is effected in this case within a very short time, resulting in a hydraulic shock within the valve. This brings about unwanted oscillation of the valve member and of the relief piston at a relatively high frequency, which accelerates the wear of practically every major component of the hydraulic lock, thereby shortening the service life thereof.